It is known that in trunk exchanges every call monitor generating signals for periodic counting (such as conventional duration and area counters or emitters of metering pulses) is associated with so-called statistical counters which, on the basis of the circuit conditions characterizing the different stages of a call, totalize the number of engagements, the number of effective calls, the duration of each call and the number of counting pulses for the traffic associated with a given call monitor.
The reading of data from statistical counters allows to obtain direct information on the traffic associated with the respective call monitors, e.g. information concerning the average traffic during certain time intervals, the traffic allotted to various parts of the exchange, or the origin of the traffic. In addition, such data can give indirect information on service quality (e.g. the number of successful calls), and on the correctness of operation of the call monitors to which the counters are connected.
Moreover, statistical counters can provide data necessary for profit sharing, as needed when several companies combine to provide telephone service within a given country.
At present such data are obtained by periodically photographing the counters and by transcribing data in a form and on a carrier which can be read by a processor arranged to derive from these data the information necessary for the administration of the service.
This method of operation presents many serious disadvantages.
It is very expensive, since it requires a lot of labor for data collection, photograph development, and data transfer in a form and onto a carrier suitable for reading by the processor.
For this reason, the data collection is normally carried out only at rather long intervals (e.g. monthly) and, as a consequence of the length of time needed for a data-collection operation, the available information is very seldom up to date.
A further consequence is that failures of the counters or of the call monitors to which they are connected are discovered only after considerable delays.
Moreover, such data-collecting techniques provide results which are not sufficiently reliable, both because of the intrinsic nature of electromechanical counters, which are highly susceptible to wear, and because of the large number of processing operations required which tends to increase the error probability.
For this reason, after a data-collection operation, if the data obtained are sufficiently different from a predetermined allowable range of values considered as indicating probable correct operation of the call monitors associated with the exchange, it is necessary to carry out a series of checks in order to establish whether the discrepancy is due to real operating anomalies of the call monitors or to inadequate data collection. It is evident that the need for such checks not only increases the intervals at which such data are made available but also raises the total cost of the data-collection operations.
Another disadvantage of the present way of reading data from statistical counters is that, as such counters are all located near the associated trunk exchanges, it is practically impossible to obtain simultaneously data relating to the entire country.
In commonly owned copending application Ser. No. 833,363, filed by me jointly with two others on Sept. 14, 1977, now U.S. Pat. No. 4,165,447, there has been disclosed an apparatus designed to automatize these operations, i.e. to obtain data relating to traffic directly from call monitors energizing mechanical statistical counters and to preprocess such data relating to traffic so as to make them directly utilizable by the processor.
To this end, the apparatus described in that prior patent includes a synchronous preprocessor (having an operating cycle in which respective time slots are allotted to sensors to be supervised) designed to measure the duration and count the number of events associated with the state of each monitored signal path and to emit, in message form, significant data relating to each call monitor. This task is accomplished by the use of sophisticated preprocessor equipment arranged to handle, without loss, data from a multiplicity of sensors. Such an apparatus is well adapted to the characteristics of available processing systems; the unit cost of the processing operations is reduced to a minimum, and the sensors serving to detect the states of the monitored signal paths can be scanned in a time-multiplexing mode to report the signals present at their inputs. Thus, such sensors could be easily located far from the preprocessor since the connections require but a small number of wires; besides, the communications between sensors and preprocessor are of a limited nature so that each information can be detected by its time location, hence the structure of the data-collecting devices can be rather simple.